This project is designed to achieve a better understanding of how the cellular repair capacity, the nature and extent of DNA damage and cellular metabolism interact to determine the biologically important endpoints of survival and mutagenesis. The work reported in this project involves the genetical and biochemical characterization of the DNA repair processes involved in error avoidance and error fixation. In particular, we have investigated the affect of dose on mutational specificity in order to learn more about what mutational events occur as different cellular repair capacities become saturated. This data not only will provide a basis for an improved understanding of the mechanism by which mutation occurs but will also lay the groundwork for a more accurate understanding of low-dose effects and their associated risks.